Engine rotational speed information, (e.g., the speed of the crankshaft), may be needed for the control of engine operation, such as determining proper spark and fuel injection timing, gear shifting in automatic transmissions, etc. These control functions may require the average engine speed value over no less than one full revolution. The actual engine speed, however, is not constant. Even in a steady state, an internal combustion (IC) engine generally exhibits cyclical speed variations attributable to the operation of its cylinders. Each individual cylinder slows the engine during its compression cycle and speeds it up during its power cycle.
In the field of vehicular diagnostics, accurate instantaneous engine speed information enables the detection and diagnosis of many engine problems, even subtle ones. See, for example, U.S. Pat. Nos. 4,539,841 and 4,520,658, respectively titled “Method For Determining Engine Cylinder Compression Pressure and Power Output” and “Method For Locating Engine Top Dead Center Position,” for some exemplary engine diagnostic applications that use instantaneous engine speed information. Presently, there is a limited choice in the ways of obtaining such information. For example, it is known that one can tap into the crank sensor wiring, or use a separate, intrusive sensing technique, such as mounting a sensor in the bell housing to sense the rotation of the ring gear.
Shortcomings of the first approach for obtaining instantaneous engine speed information may include burdensomely locating and gaining access to the crank sensor connector, the location of which connector typically varies from vehicle to vehicle. This generally results in incremental costs since even just a few additional minutes per vehicle cumulatively may add up to substantial costs when servicing a large number of vehicles. Secondly, the characteristics of the crank position signal commonly differ from one vehicle to another in terms of signal resolution (e.g. 6×, 24×, 60×), coding and format (e.g., analog or digital format). Similarly, costly and time-consuming inefficiencies may arise with the second approach for obtaining instantaneous engine speed information since intrusive sensing of engine speed is generally not conducive to quick and cost-effective servicing and/or diagnostics operations, and often requires costly vehicle modification.
What is desirable is a non-intrusive, user-friendly, easily attachable/detachable low-cost and reliable sensor assembly that would provide accurate instantaneous engine speed information. It would be further desirable to provide sensing techniques and sensor assembly that would result in highly accurate instantaneous engine crankshaft speed information independently of the crankshaft sensor of the engine. It would be further desirable to provide sensor assembly and sensing techniques that would allow for accurately detecting variation of engine speed as well as the magnitude of the engine speed itself. It would be also desirable to provide a sensor assembly that may be universally used in a wide variety of vehicular configurations without any specialized training or tooling requirements from one vehicular configuration to another.